This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 199 43 609.6, filed on Sep. 11, 1999, the entire disclosure of which is incorporated herein by reference.
The invention relates to a pre-spooling device or pre-winder for the weft thread in an air jet loom, including a weft thread storage drum consisting of plural drum segments that are each adjustable in a radial direction. The weft thread is wound onto the drum segments by a thread guide cooperating with a drive shaft, and is then drawn of f from the drum segments by the weft insertion means that carry the weft into the loom shed.
It is generally known to provide weft pre-spooling devices, also known as weft thread stores, for air jet looms, to continuously draw-off the weft thread from the main supply spool, and to make ready a predetermined adjustable length of yarn or thread for each weft insertion of the weft thread into the loom shed. In practice, it is known to use pre-spooling devices with so-called drum stores, for example as disclosed in German Patent Laying-Open Document 35 34 599, published on Apr. 30, 1986. Typically, as disclosed in this reference, the proper length of weft thread is preselected, wound up on a drum, and then intermediately stored on this drum. The weft insertion length is determined by the circumference of the drum multiplied by the number of windings or turns of the weft thread around the drum as provided for each respective weft insertion.
Thus, the length of weft thread provided for each weft insertion can be adjusted in discrete steps by adjusting the number of turns or windings of the weft thread provided on the drum. A further possibility of adjusting the weft insertion length is provided in that the drum consists of plural drum segments distributed about the circumference of the drum. The drum segments are each radially adjustable, whereby a radial sliding adjustment of the drum segments changes the diameter and the circumference of the drum, which thereby also changes the length of each winding or turn of thread and consequently adjusts the total weft insertion length provided by a prescribed plurality of such thread windings. Interspaces or gaps are formed between the successive drum segments distributed about the circumference of the drum, whereby these interspaces become larger or smaller depending on the radial adjustment of the drum segments.
The action of drawing the weft thread off of the drum during the weft insertion forms a so-called thread balloon between the draw-off region of the thread leaving the drum and a drawing-off eye or eyelet arranged downstream thereof. The drawing-off eyelet can be arranged in a so-called balloon breaker or anti-ballooning device, which limits the formation and radially outward extent of the balloon. Alternatively, the drawing-off eyelet can be mounted on a separate holder bracket or can be connected directly to the weft insertion nozzle.
The form or shape of the thread balloon depends on various parameters. The thread characteristics have a considerable influence on the formation of the thread balloon. For example, smooth filament yarns lead to the formation of a larger thread balloon, whereby it is advantageous for the weft insertion to limit the formation of such a larger thread balloon by means of the balloon breaker or anti-ballooning device. Voluminous yarns or yarns with a band-shaped or ribbon-shaped cross-section, however, exhibit a higher form resistance in the air and in the rotation direction, whereby a smaller thread balloon is typically formed. In that case, the thread has a tendency to enter into the open interspaces or gaps between the drum segments during the drawing-off of the thread from the drum. The thread then collides with or catches on the rounded edges or corner portions of the respective drum segments as the thread is unwound from the drum.
When the thread enters the interspaces in the above mentioned manner, this causes energy losses in the thread during the weft insertion and during the transport of the thread across the weft thread insertion length. Furthermore, that also causes interferences in the proper insertion and transport of the weft thread, which in turn tends to increase the time window or time spread during which the weft thread will arrive at the downstream or arrival side of the loom. This increases the difficulty of detecting whether a weft fault has occurred. In order to ensure the proper and trouble-free operation of the loom in this case, a higher energy must be applied to the thread, and/or the rotational speed of the loom must be decreased. Both of these measures have a negative influence on the efficiency of the loom and the weaving process.
In view of the above, it is an object of the invention to provide a weft pre-spooling device or pre-winder of the above mentioned general type, which is improved in such a manner so as to achieve the interference-free drawing-off of the weft thread, and particularly a weft thread having a high inherent form resistance, so as to avoid the above mentioned disadvantageous effects on the operation of the loom. Particularly, it is an object of the invention to provide such a pre-spooling device from which the weft thread can be smoothly drawn off, without becoming caught in the open interspaces or gaps between adjacent drum segments. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as are apparent from the present specification.
The above objects have been achieved according to the invention in a pre-spooling device including a weft storage drum comprising a plurality of drum segments that are each adjustable in a radial direction, a thread guide that is connected to a drive shaft and is adapted to wind weft thread onto the storage drum, and a protective disk arranged in the area of the downstream or drawing-off endface of the drum. A weft insertion mechanism is adapted to draw the weft thread off of the storage drum and carry it into the loom shed. The protective disk is arranged so that the weft thread is drawn off over the circumferential edge of the protective disk.
The key concept of the invention is to prevent the penetration of the weft thread into the open gaps or interspaces between the successive drum segments by arranging the rotationally symmetrical protective disk in the area of the downstream or drawing-off side endface of the drum. The weft thread is then drawn off over the circumferential edge of this protective disk. This arrangement makes sure that the weft thread is held away from the circumference of the storage drum, especially near the downstream end thereof, and thereby prevents the thread from penetrating into the open gaps between adjacent drum segments or becoming caught on the free edges of the drum segments.
Preferably, the diameter of the protective disk corresponds approximately to the respective prevailing diameter of the drum, i.e. the diameter to which the drum segments are adjusted at a given time. Due to the possible diameter variation of the drum as the result of the radial adjustment of the drum segments, the invention further provides for an exchangeable set of protective disks having respective different diameters. Thus, the particular protective disk is exchangeable to match the adjusted diameter of the storage drum. Also, the axial spacing distance of the protective disk away from the endface of the storage drum is adjustable. By the above measures, the diameter of the disk can be adapted to the actual presently existing diameter of the drum.
In order to reduce the frictional resistance between the weft thread and the protective disk, the circumferential edges of the protective disk are rounded-off. Moreover, preferably the edge or perimeter surfaces of the protective disk have a selected surface roughness or smoothness characteristic in a range from rough to smooth, depending on and corresponding to the quality of the yarn that is to be processed.
In a first example embodiment, the protective disk is connected rigidly to a non-rotating part of the pre-spooling device or pre-winder, for example, such as the drum of the pre-spooling device. Thus, the protective disk is stationary or fixedly arranged and the weft thread glides over the outer perimeter surface of the protective disk while it is being drawn off. In order to further reduce the frictional resistance between the weft thread and the protective disk, a second example embodiment provides that the protective disk is rotatably driven to rotate about its center axis, whereby the protective disk is connected to the drum or to the drive shaft of the thread guide. In this context, the rotational direction of the protective disk corresponds to the rotational direction of the thread guide. In other words, the rotational direction of the protective disk is the same as that of the rotating elements of the pre-spooling device. In this manner, the frictional resistance can be substantially reduced, which is especially advantageous when sensitive yarns are being processed. Preferably, the rotational speed of the protective disk is adjustable, so that it can be adapted or matched to the drawing-off speed of the yarn.
A variation of the drive mechanism is that the protective disk is rotationally driven by wings or vanes that are arranged on the protective disk, whereby an appropriately arranged blowing nozzle blows a pressure medium against these wings or vanes in a tangential or circumferential direction so as to rotationally drive the protective disk. In a second variation of the drive mechanism for the protective disk, the disk is driven directly by the drive shaft which also rotatingly drives the thread guide. In a third drive variation, the protective disk is driven by an electric motor, which is arranged rigidly on a non-rotating part of the pre-spooling device, such as the drum, for example.
Preferably, the protective disk essentially consists of or comprises a light metal alloy such as an aluminum alloy, or a synthetic plastic that is provided with a hard coating.